Liquid crystal displays (LCDs) have many advantages such as thin body, low power consumption and no radiation, and are widely used in mobile phones, personal digital assistants (PDAs), digital cameras, computer panels and panel of notebook and so on.
Most liquid crystal display devices on the market are backlight type liquid crystal display devices, which include a housing, a liquid crystal panel disposed in the housing, and a backlight module disposed in the housing. The structure of a conventional liquid crystal panel is composed of a color filter substrate, a thin film transistor array substrate (TFT Array Substrate), and a liquid crystal layer disposed between the two substrates. The working principle is that the driving voltage is applied to the two substrates to control the rotation of the liquid crystal molecules of the liquid crystal layer, and the light of the backlight module is reflected to generate an image. Since the liquid crystal panel itself does not emit light, the light source provided by the backlight module needs to be used to display the image normally. Therefore, the backlight module is one of the key components of the liquid crystal display device. The backlight module is divided into an edge-type backlight module and a direct-type backlight module according to different positions of the light source incident. In the direct-type backlight module, a light source such as a cold cathode fluorescent lamp (CCFL) or a light emitting diode (LED) is disposed behind the liquid crystal panel, and the surface light source is directly formed and provided to the liquid crystal panel. The edge-type backlight module is provided with a backlight source LED light bar located at the edge of the backplane disposed on the lateral back of the liquid crystal panel. The light emitted by the LED light bar enters the light guide plate (LGP) from a side of the light incident surface of the light guide plate, and is emitted from the light emitting surface of the light guide plate after reflecting and diffusing, and then passed through the optical film set to form a surface light source provided to the liquid crystal panel.
As higher and higher requirements to the appearance of television (TV), notebook computers (laptops) and other electronic display products by the consumers, more and more consumers pay more attention to the slim design and narrow bezel design of TV sets. Currently, the edge-type backlight module can quickly achieve thin TV by ways to reduce of LED size, light guide plate thickness, film thickness or the use of full Lamination and occupy the field of ultra-thin TV market. However, since the price of the light guide plate in the edge-type backlight module is relatively high, and the number of LED chips used is relatively large, making it easier to reach a thin profile, but it has no cost advantage and cannot be implemented at the low-end consumer groups to have a wide range of markets. Compared with the edge-type backlight module, due to the lower price of the diffusion plate of the direct-type backlight module in same size, the number of LED chips used is relatively small to have a clear price advantage, but due to design limitation, the closer the distance of the diffusion plates and LED, the LED mura is more likely to be generated, and the taste is poor. If the direct-type backlight module needs to pass the taste, it needs to ensure sufficient optical distance (OD) between the diffusion plate and the reflective sheet, or by increasing the number of LED to prevent the emergence of the problem. However, increasing the OD value will result in a larger thickness, resulting in the direct-type backlight module cannot get the ultra-thin TV market. Increasing the number of the LED will increase the cost and weaken the cost advantage of the direct backlight module.
FIG. 1 shows the principle of generating the mura problem in the direct-type backlight module, and FIG. 2 shows a schematic view of the mura phenomenon occurring in a light emitting surface of a direct-type backlight module. As shown in FIG. 1, the principle of the mura problem is: since the light emitting angle of the LED lamp 610 has a limitation, non-luminous dark areas between the adjacent LED lamps 610 and the light emitting area of the nearby LED lamp 610 form an image with uneven brightness and darkness, after the light passes through the diffusion plate 500 and the optical film 800, the diffusion plate 500 and the optical film 800 have a certain diffusion effect on the light, but are not enough to change the unevenness of light and darkness, thus causing the problem of mura. At present, the solution to the mura problem is to reduce the LED spacing or increase the OD value. Both of these methods have disadvantages. The first method needs to increase the number of LED lamps 610, thereby increasing the backlight module cost. The second method is unfavorable to ultra-slim design, and affects TV appearance. Therefore, there is an urgent need in the industry for a solution to the mura problem without increasing the number of LED lamps 610 and increasing the OD, so as to realize the low cost and ultra-slim design of the direct-type backlight module, and further achieve the slim design of the entire TV set.